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Flashcards in NEETS Mod 5 - AC Generators Deck (24)
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1

What are AC generators generally known as?

Alternators

2

What principle do all electrical generators depend upon?

Magnetic Induction

3

What are the two ways EMF is induced in a coil?

(1) a coil cutting through a magnetic field
(2) a magnetic field cutting through a coil

4

Magnetic Induction occurs when there is relative motion between what two elements?

Conductor and magnetic field

5

What is the part of an alternator in which the output voltage is generated?

Armature

6

What are the two basic types of alternators?

Rotating armature
Rotating field

7

What is the main advantage of the rotating field alternator?

Output voltage is taken directly from the armature (not brushes or slip rings)

8

What are the two types of rotors used in rotating-field alternators?

Turbine-driven
Salient-pole

9

When is a turbine-driven rotor used?

When the prime mover is a high speed turbine.

10

When are salient-pole rotors used?

In low-speed alternators

11

How are alternators usually rated?

By the voltage and maximum current they are designed to produce. (volt amperes)

12

What type of prime mover requires specially designed high-speed alternator?

Steam turbine

13

Salient-pole rotors may be used in alternators driven by what types of prime movers?

Low speed (portable tools & small appliances)

14

What does single phase indicate?

One continuously alternating voltage (output)

15

What is the most common alternator used today?

Three phase

16

What determines the phase relationship between the voltages in a two phase AC generator?

Placement of the armature coils

17

In a three phase alternator, what is the phase relationship between the individual output voltages.

Each phase is displaced 120°

18

What are the two methods of connecting the outputs from a three phase alternator to the load?

Delta & Wye

19

What type of transformers and connections are used to convert 450v, 3 phase power to 117v, single phase?

Single phase, step-down transformer

20

What two factors determine the frequency of the output voltage of an alternator?

Number of poles (NP), multiplied by
Speed of rotation, divided by 120.

21

What is the frequency of the output voltage of an alternator with four poles that is rotated at 3600 rpm?

4 × 3600 = 14,400

14,400 ÷ 120 = 120

22

The variation in output voltage as the load changes is referred to as what? How is it expressed?

Percentage of regulation

23

How is output voltage controlled in practical alternators?

By varying the voltage applied to the field windings.

24

What generator characteristics must be considered when alternators are synchronized for parallel operation?

Output voltage, frequency, and phase relationships.